For separating ingredients contained in fluid such as liquid and gas, various methods have been proposed. For example, in the recent technique for removal of ionic substances contained in seawater, brackish water or the like, separation methods utilizing separation membrane elements have found increasing uses as processes for energy savings and conservation of resources.
Separation membranes adopted in the separation methods utilizing separation membrane elements are classified into groups of microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes and forward osmosis membranes, based on their pore sizes and separation performance. These membranes have been used in e.g. production of drinkable water from seawater, brackish water or water containing deleterious substances, production of ultrapure water for industrial uses, effluent treatment, recovery of valuable substances, or the like, and membranes to be used therein have been changed to suit the ingredients targeted for separation and separation performance requirements.
Separation membrane elements have commonality in the sense that a raw fluid is fed to one surface of a separation membrane and a permeated fluid is obtained from the other surface of the separation membrane. By having a plurality of separation membranes tied in a bundle, each separation membrane element is configured to secure a large membrane area to give a large amount of a permeated fluid per the unit element, and various types of elements, such as those of a spiral type, a hollow fiber type, a plate-and-frame type, a rotating flat-membrane type and a flat-membrane integration type, have been produced in accordance with their intended uses and purposes.
For example, spiral-type separation membrane elements have been widely used in reverse osmosis filtration. The spiral-type separation membrane element is provided with a perforated water collection tube, a feed-side channel member for feeding a raw fluid to a separation membrane, a separation membrane for separating ingredients contained in the raw fluid, and a permeate-side channel member for leading the permeated fluid that has permeated through the separation membrane toward the perforated water collection tube. The feed-side channel member, the separation membrane and the permeate-side channel member are wound around the perforated water collection tube. The spiral-type separation membrane element applies pressure to a raw fluid to thereby take out a permeated fluid in greater quantity, and is therefore used widely.
With the recent increase in the demand for reduction in water production cost, a need for cost reduction in producing separation membrane elements is increasing, and cost reduction by improving separation membranes, channel members and separation membrane element members has been proposed. For example, in Patent Documents 1 to 3, in a spiral-type separation membrane element, there are provided channel members arranged in a dot-like or stripe-like pattern on the front surface or the back surface of a flat membrane. In Patent Document 4, there is provided a channel membrane formed of a fibrous substance on a sheet.